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Seasonal changes in hydrology and the distribution of plankton
in the Bathurst Harbour estuary, southwestern Tasmania, 1988-89

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Edgar, GJ and Cresswell, GR 1991, 'Seasonal changes in hydrology and the distribution of plankton
in the Bathurst Harbour estuary, southwestern Tasmania, 1988-89', Papers and Proceedings of the Royal Society of Tasmania, vol. 125, pp. 61-72.

Abstract

The hydrology and abundance of planktonic organisms (>20 m size) were surveyed at various sites in the Bathurst Harbour/Port Daveyestuary on five occasions between October 1988 and July 1989, and the hydrology again surveyed in February 1991. In winter, the periodof peak freshwater outflow, a brackish surface layer (~15%0) was present to a depth of ~4 m throughout the estuary. This surface layer waspresent to a reduced depth in other seasons, except during summer, when the halocline broke down and surface salinities of ~29%0 in 1989and ""25%0 in 1991 prevailed. Bottom waters were close to fully marine (~33%0) throughout the year. Surface waters in Bathurst Harbourwere found to be extremely depleted in nitrates «0.1 11M). Oxygen levels were also very low (~35% saturation) during the 1989 summer,which was unusually dry, but were near full saturation during the other sampling periods.The plankton community in Bathurst Harbour contained very few taxa, particularly during the winter months. The dinoflagellateDinophysis acuminata comprised >99% of total phytoplankton numbers in October 1988 and July 1989, while the copepods Gladioferensinermis and Oithona australis and the appendicularian Oikopleura sp. numerically dominated the woplankton community. Dinoflagellatesand copepods both occurred in high densities. The distribution of diatoms within the estuary was inversely related to the distribution ofdinoflagellates; diatoms occurred in low densities relative to dinoflagellates in Bathurst Harbour outside the summer months, but occurredin much higher densities than dinoflagellates in the waters of Port Davey throughout the year.